Project Summary There is a critical developmental window for maturation of social functioning. Harmful social experiences during this time can produce life-long social impairments, and contribute to mental illness. This may be due to effects of the social environment on the development of key brain regions involved in complex social behaviors, such as the amygdala. The long-term goal of our research is to understand how social experience during development shapes the function of the amygdala and interconnected regions, and how dysfunction in these circuits produces social impairments. Social function requires a balance between the drive to engage in social behaviors and normal social caution in ambiguous social situations. The short-term goal of these experiments is to test whether the balance between social drive and social caution changes during development, whether medial amygdala (MeA) function underlies this balance, and whether disruption of social development impairs this balance of MeA function. This project will test the hypothesis that there is lower social caution during the prepubertal period and immaturity of MeA outputs to brain regions that engage social caution. The balance between social drive and social caution is sensitive to social conditions. This project will also test the hypothesis that conditions that promote social drive activate MeA outputs to brain regions that promote social behaviors, and that the balance between social drive and social caution is disrupted by harmful developmental social experience. The Aims of this project are to determine if social function shifts from social drive towards social caution across development, if the balance between MeA output paths shift across development, and if disruption of social development impairs the balance between social drive and caution. This project will compare the mechanisms that regulate MeA activity and social behavior across age. This project is significant because it can uncover a novel neurobiological mechanism for differences in the balance of social drive and social anxiety across age, and novel mechanisms for the effects of harmful social experience on the neural substrates of social behaviors. These experiments are innovative because they will examine the role of amygdala development in social behavior in the context of a new functional framework. This approach will yield exciting new information about the development of social behavior in parallel with the development of MeA circuits. This project will lead to novel insight about social development, and how social experience can produce social withdrawal and anxiety, major symptoms in several mental illnesses.